1. Field of the Invention
The invention relates to a coolant conduit comprising a plurality of polymer layers that has a high resistance to hydrolysis and a high resistance to pressure which conveys a high bursting strength. In particular, the invention relates to a coolant conduit which is an elongate tubular article for an apparatus such as an engine, for example, an internal combustion engine, of a vehicle requiring cooling by a cooling agent.
2. Description of the Related Art
Coolant conduits do not have simple shapes as a rule, but rather have bizarre shapes and are often constructed from metal parts and elastic intermediate parts in order to compensate for vibration of the engine which can sometimes be very intense. In accordance with the prior art, rubber conduits reinforced with woven fibers (textiles) have been used for this purpose. Such rubber conduits have been preferably used for vehicle engines but have the disadvantage that they are relatively expensive and, despite this, do not completely fulfill the requirements, particularly with respect to stability at the high temperatures occurring in an engine compartment. The mechanical properties of such rubber coolant conduits deteriorate sharply after a vehicle engine service life corresponding to approximately 100,000 kilometers traveled. Stability of such rubber coolant conduits for future automobile engines will become even more critical, because future automobile engines will allow the temperatures in the engine compartment to rise even higher than they have up to now thereby accelerating deterioration in the mechanical properties of coolant conduits.
Cooling water conduits composed of a single polymer layer, so called "monotubes", have only been used to a limited extent up to now. At temperatures above 100.degree. C., monotubes made of polyolefins exhibit an inadequate pressure resistance. At temperatures above 100.degree. C., monotubes made of polyamides exhibit a reduced resistance to hydrolysis.
For this reason, polyamide reinforced with glass fiber has preferably been used up to now for parts that come directly into contact with coolants, because the glass fibers can partially compensate for the loss of mechanical properties of the polyamide, e.g., due to swelling. Glass fiber-reinforced conduits are often insufficiently flexible.
Tubular, multilayer coolant conduits are known and have been produced by coextrusion according to EP 0 436 923, the disclosure of which is incorporated herein by reference. These coolant conduits have corrugated walls and are flexible, but have only limited application, however, because their use is limited by the polymer combination selected.
It is therefore an object of the present invention to create a coolant conduit that does not have the forenamed disadvantages.